How laundry dries

One thing that bothered me while living in Australia was drying laundry. Many rental properties do not contain a clothes dryer and people tend to avoid using dryers when they are available. I like dry laundry. Even on intensely sunny days in Australia, drying clothes on a line never seemed to eliminate all the moisture content. People claim sun dried laundry has a fresh smell. To me, it smelled like faint dampness.

I recently took a stab at quantifying the effect. The experiment consisted of hanging wet laundry outside and measuring its weight over time. As a shirt dries it loses water content and its weight decreases. Here is the data:

We observe that the Merino wool shirt dried quicker than the cotton shirt. Wool dries faster than cotton. The Merino shirt weight took around 60 minutes to stabilize. The cotton shirt dried in around 90 minutes. However, when I put the shirts in the clothes dryer for 15 minutes, both their weights decreased. This suggests there is additional dampness in the clothing that air drying alone cannot eliminate. The data supports the conclusion that air drying clothes will not make them as dry as a clothes drier will.

Interestingly, it appears that an optimum way to dry your laundry with respect to energy use and time is the following: line dry your clothes for 90 minutes and put them in the dryer for 15 additional minutes. It’s also possible that tumbling clothes in a mesh tub outside may dry them quickly without using any additional heat energy. This would save the hassle of hanging them on a line.

Addendum: I dug the shirts out the following day and weighted them again. Both shirts gained about 4 grams in water content. However, their weight was still 3-5 grams less than their line dry weight.